How Does the Brain Work?

Neurons and Axons

The specialized cells called “neurons” that do the processing work of the brain (such as thinking) are most highly concentrated in the outer layer of the cortex, known as the gray matter. The neurons also exist in dense clusters within the white matter of the brain. The axons (which are long, hollow tubular structures) form the “wiring” or neurological circuitry that links neuronal processing centers. These axons carry neural messages at speeds of 1/10,000th of a second, because they are coated with a fatty substance called myelin that functions like a conductive insulation material.

The nerve impulse starts as an “action potential,” an electric charge that goes down the axon and triggers the release of chemical substances called “neurotransmitters” to flow across the gap between one axon and 100 to 10,000 dendrites arrayed to receive chemical messages . The precise alignment of these axon – dendrite connections or “synapses” is the product of genetics and environmental influences, that incorporate what we have learned and what our central nervous system remembers.

Vulnerability to Trauma

The human brain is vulnerable to trauma, both mechanically (due to the initial trauma) and chemically (secondary to the trauma). Both can change how and what we perceive, remember, think, feel and act. Brain chemistry may be radically altered by microscopic damage to the axons of the brain that is not detectible on modern MRI or CT scans.

This is a huge problem both clinically and legally. Physicians and lawyers who do not understand these microscopic changes often judge victims of “mild traumatic brain injury” (mTBI) with negative results on MRI and CT as faking, exaggerating, or over-reacting to a blow to the head. And you can be certain the insurance company will call a doctor as a witness at trial to say exactly that. What is often heard in the defense doctor testimony is that both a head strike and a loss of consciousness during the impact are necessary for any brain injury. This is simply not supported by the modern brain injury research and the US National Institutes of Health has actually issued a position paper stating this is not the case. Still insurance doctors will use this tactic to try to mislead jurors.

Advanced Brain Imaging Techniques

There are discussions in the medical community presently that more advanced imaging may detect disturbances of normal brain chemistry with functional imaging techniques including PET scans, fMRI and MRI spectroscopy. These can show major disturbances of brain metabolism in mild TBI patients. Unfortunately these scans are very expensive and are not presently available in Oregon or many other parts of the US. In many cases, even when the units are available, the radiologistwho works with the unit is not accustomed to looking at brain images, as the PET and SPECT scans are most often used to monitor Cancer, not brain injuries.

High Speed impacts to the Brain

High speed impact to the skull is associated with a high degree of physical compression and torsion of brain tissue and concussion of the brain against the skull wall. Often, this results in grossly visible changes of brain structure. These type of injuries include bleeding contusions to the brain surface, deep hemorrhagic lesions, epidural or subdural hematomas. These changes to normal brain architecture are visible on CT or MRI.

Depending on which direction the blow comes from, the brain can be damaged on top, from the front, from the back, from below, from either side, or in a combination of areas.

Frontal Lobe Injuries

Many brain injuries affect the frontal lobes. The frontal lobes which occupy approximately 1/4rd the volume of the adult human brain, lie behind the forehead and the eyes. They are the control center for our “executive functions.” When we are confronted with a stimulus (such as a social interaction with family, a job interview, or a first date) we use our frontal lobe to evaluate the situation. It considers our options in the context of social norms, our immediate goals and motivations, and the expected consequences. It helps us plan a response, issues commands to our muscles of speech and movement, monitor the outcome; and changes our course of action based upon the feedback. Brain injuries often affect the frontal lobes, because car accidents tend to involve contact between the forehead and a hard surface. In such injuries, the inner surface of the skull next to the frontal lobes contains a series of sharp, knife-like ridges. This type of impact, and the cognitive deficits which arise from it are often called Post Concussion Syndrome.

Frontal lobe injuries not only interfere with planning, execution and monitoring of everyday tasks, but also reduce motivation and cause apathy. People with frontal lobe injury often know what to do, but cannot accomplish their goals due to a “break in the connection” between acquired knowledge and skills, and the capacity for action.

Shaking or Striking Injuries to the Brain

The exterior of the brain is vulnerable to focal contusions (bruises) from shaking or striking of the head, which bounces the brain against the inner walls of the hard skull. If the contact of brain against skull is hard enough the brain may swell up until it is crushed against the confines of the cranium, which will compress cerebral arteries and cause oxygen deprivation injury (anoxia) similar to stroke, unless the swelling is rapidly reversed by surgery. The interior of the brain is vulnerable to damage from stretching and tearing of axons, known as diffuse shear. Areas of the brain where shearing is particularly likely to occur include the gray matter / white matter boundary and the corpus callosum.

When trauma to the brain causes rupture of blood vessels, an epidural, subdural or subarachnoid hemmorhage will result, depending upon where the vessels break. These bleeds may occur slowly or quickly, and may cause small, medium or large collections of blood, with characteristic shapes, depending on the specifics of the trauma. CT scan is excellent for detecting a bleed. A large bleed will lead to obvious disturbances of consciousness such as blank stare, slurred speech, dilated pupils, lethargy, etc., and will require a craniotomy to remove a clot, or suction the liquid blood.

The inner and outer portions of the brain have different densities. Trauma which rapidly jerks the head around and which exerts rotational force on the brain, makes the inner and outer portions move at different velocities, and this can damage axons at the gray-white matter interface by mechanical stretch.

Blunt Brain Trauma Injuries

Direct, blunt trauma (such as the head hitting a sidewalk or the B pillar inside a car) causes an initial contusion to the outside of the brain closer to the blow – the coup – followed by linear acceleration of the brain into the opposite skull wall, where another contusion results called the contre coup. The same traumatic event (such as a car crash) can cause one or both types of damage.

If the blow to the head is hard enough, the skull will cave inward and break into fragments, which dig into the brain and cause bleeding. This is known as a depressed skull fracture, and is associated with an elevated risk of epilepsy. High speed car crashes (those at 60-80 mph) and other highly forcible impacts to the head, can send shock waves through the brain and so deform its inner structures, as to cause death, permanent vegetative state, hydrocephalus (ventricular blockage) or severe dementia.

The smallest functional unit of the brain is the individual nerve cell or “neuron.” Infants are born with over one hundred billion neurons. Neurons need a constant supply of oxygen and glucose to survive and remain vulnerable throughout the human lifespan to damage or death by traumatic events which cut off the supply of oxygen or glucose. These can range from cranio-cerebral traumas such as that caused by a collision.

Closed Head Injuries

Most traumatic brain injuries are “closed head,” meaning the skull has not been openly penetrated by a knife, bullet or other object or been fractured into the brain tissue by collision with a hard, unyielding object. Closed head brain injuries tend more towards being “diffuse” and involving more generalized or “global” disruption of brain function. Global disruption is rarely evident in a standard neurologic exam of mental status, motor control, reflexes and sensation, and more likely to be detected by neuropsychological evaluation of cognitive functioning.

Only In its most severe form is diffuse injury obvious on MRI and fatal. In its milder and more common form, diffuse brain injury injury is barely detectable or not detectable at all on MRI, and its manifestations can be confused with depression, chronic fatigue, attention deficit disorder, somatiform disorder, hysteria or malingering. What is often called “mild traumatic brain injury,” is in actuality a significant injury to the brain which has not been accompanied by obvious structural damage to anatomical landmarks.

Post Concussion Survey

One basic way to consider the symptoms of a traumatic brain injury are to take the Rivermead Post Concussion Symptoms survey, which is available here.

Brain Injury Lawyers

At Dr. Aaron DeShaw, Esq., P.C., we handle many brain injury cases every year to a successful conclusion. We understand the problems associated with these injuries, and counsel clients and their families through the serious changes that take place after a brain injury. We also work on large cases nationally, when you want a lawyer with a medical background in brain injury diagnosis.

If you, a friend, or family member have sustained a brain injury as a result of another’s negligence, call us today toll free at (866) THE-FIRM, or contact us by e-mail. The phone call, and the initial lawyer consultation are both free.